Mistletoe is a name used for a variety of different plants across the world, but in Britain it generally means European mistletoe (Viscum album), a semiparasitic plant that grows on the branches of trees. Being semiparasitic means it takes water and some of its nutrients from the tree on which it grows, while also capturing its own energy through photosynthesis.
This unusual feature allows mistletoe to thrive high in the tree canopy, but also makes it dependent on both suitable host trees and the animals that help it reproduce.
Mistletoe is best known today for the tradition of kissing beneath it at Christmas, a custom that became popular in the 19th century. The plant also features in Greek and Norse mythology and has some tenuous associations with ancient druidic practices in Britain.
These cultural associations have helped cement mistletoe’s image as a plant of tradition, protection and continuity, even as its ecology proves surprisingly dynamic.
A complicated life
Mistletoe’s life cycle is more complicated than the average plant. It’s among the 6% or so of flowering plants where male and female flowers grow on separate plants. Both produce tiny green flowers that smell sweet and fruity to attract pollinators such as flies and bees. The female plant grows white berries which are coated in a sticky substance called viscin.
Seeds tend to be dispersed by birds. Species such as mistle thrushes, waxwings and blackcaps eat the berries and then either poop seeds out or wipe them off their beaks and feet onto nearby branches. The sticky coating helps the seeds adhere to the bark, where they can germinate.
The fact that it has separate male and female plants, and its reliance on birds, makes mistletoe surprisingly slow to spread. If a lone plant is growing in a new location, it could be years before more arrive. These biological constraints have traditionally limited mistletoe to places with the right combination of climate, host trees, pollinators and seed dispersers.
Orchards to gardens
Mistletoe is most commonly associated with orchards, especially apple trees, though it can also grow on poplars, lime, hawthorne and willow, and very rarely on oak. It is found all across England, but is most abundant in the south-west midlands. The plant is the official county flower of Herefordshire, where it has long been associated with the county’s orchards.
Over the 20th century, however, the National Trust estimates that 56% of England’s traditional orchards have vanished. You might expect this would mean wild mistletoe is in trouble – at least in England.
But that’s not the case. Its conservation status in Britain is “least concern”, and although it is often found in orchards, mistletoe is now most common in gardens. Its abundance in the south-west midlands of England could be more due to a wet and warm climate than the presence of orchards.
There have been reports of mistletoe spreading quickly in places such as Essex and Cambridge. Blackcaps, a key disperser of mistletoe seeds, have only recently started overwintering in Britain. Warmer winters have altered their migration, increasing the time they spend in the UK and therefore the time they have to spread mistletoe seeds. Changes in bird behaviour linked to climate change may therefore be affecting the distribution of one of Britain’s most familiar plants.
If you would like to get involved with mistletoe research, there is a citizen science project run by the TreeCouncil called MistleGO! in which you can record sightings, helping researchers to track its distribution. You can also buy mistletoe growing kits, although it is best to wait to sow the seeds until early spring – and it might be several years before your mistletoe plant is large enough to harvest for your Christmas party.
Even as its traditional orchards disappear, mistletoe will remain a festive fixture. It’s a living example of how complex interactions between different species amid climate change and changing landscapes make it hard to predict what the wildlife of the future will look like.
Adele Julier, Senior Lecturer in Terrestrial Ecology, University of Portsmouth
This article is republished from The Conversation under a Creative Commons license. Read the original article.
